#include<iostream>
using namespace std;

const int N = 1e4 + 10;
int a[N], b[N];
int n;

int check1()
{
	a[1] = 0;
	for (int i = 2;i <= n + 1;i++)
	{
		a[i] = b[i - 1] - a[i - 1] - a[i - 2];
		if (a[i] < 0 || a[i]>1) return 0;
	}
	if (a[n + 1] == 0) return 1;
	else return 0;
}

int check2()
{
	a[1] = 1;
	for (int i = 2;i <= n + 1;i++)
	{
		a[i] = b[i - 1] - a[i - 1] - a[i - 2];
		if (a[i] < 0 || a[i]>1) return 0;
	}
	if (a[n + 1] == 0) return 1;
	else return 0;
}
int main()
{
	cin >> n;
	for (int i = 1;i <= n;i++) cin >> b[i];
	int ret = 0;

	ret += check1();
	ret += check2();
	cout << ret << endl;
	return 0;
}